Agricultural or industrial utility vehicles have an engine system which includes an internal combustion engine, a cooler of a cooling circuit, a generator and a fan. The fan moves air through the cooler and is disposed adjacent to the cooler. The fan, the engine and the cooler are disposed in an engine compartment. Consequently, the fan could be disposed between the cooler and the engine or on that side of the cooler which faces away from the engine. In the latter case, the fan could be driven via a shaft which at one place is led through the cooler. The generator can be mechanically driven by the engine. The generator can be mechanically driven from a side of the engine which is other than that which faces the cooler. With the generator, electrical energy or electric power can be generated.
Engine systems of this type are known and used in passenger vehicles. In addition, these engine systems are commonly found in agricultural or industrial utility vehicles. However, at low driving speeds, high mechanical outputs must be engendered, for example in farm work with a tractor or in earth works with construction machinery. It is therefore necessary for a sufficient quantity of air to be moved constantly through the cooler with the aid of the fan. The output of the fan drive must therefore be sufficient to enable the engine to be sufficiently cooled even at low driving speeds.
Cooler fans are usually driven via a belt drive by the crankshaft of the engine. Consequently, a belt drive is normally mounted on the side of an engine which faces the cooler. With a belt or other mechanical fan drive, the cooler, because of the direct belt clutch, always has a rotation speed which is dependent on the speed of the engine, and the fan rotation speed cannot be tailored to the instantaneous cooling capacity requirement of the cooler. Fan speed could be varied with a belt adjusting gear mechanism between the belt pulley of the engine and the belt pulley of the fan. Such a solution, however, is costly and takes up a considerable installation space and is prone to repair, and involves a higher number of components.
Cooler fans in vehicles generate the air flow necessary to remove heat from the cooler or cooler element. The systems are designed for the so-called worst case, i.e. the operation of the vehicle under high load at low speeds and ambient temperatures. As already noted, the cooler fans are usually mechanically driven via a belt drive by the crankshaft of the vehicle. In order to reduce the drive output, a so-called Visco clutch, i.e. an element for the temperature-dependent rotation speed setting, is used. The rotation speed setting can be made solely in the “reduction” direction, i.e. the rotation speed of the fan is directly dependent on the rev speed of the engine, or less or zero if the Visco clutch is disengaged. This is based on the working principle of the generation of Viscous slip. A further possibility consists in the use of electromagnetically operated clutches.
Common to all previously used methods in the field of mechanical drives is the sole facility to reduce the rotation speed relative to that which would be produced by the transmission ratio of the belt drive. Hydrostatic drives can both reduce and increase the fan rotation speed. Their controllability, the usage characteristics at low temperatures, the small rotation speed adjustment range and unsatisfactory efficiency levels at higher rotation speeds constitute the associated drawbacks.
Electric fan drives are used in the automotive field. There are both two-point controller version (on/off), and rotation-speed-controlled drives in vehicles with high cooling capacity requirement. The fan drive capacities which are necessary in these vehicles amount to about 5-10% of the rated capacity of the engine and give rise to considerable requirements in terms of installation spaces and costs. Particularly, the direct drive version (i.e. the fan motor drives the fan without interposed gear mechanism) requires installation spaces which are not available in conventional engine compartments.
To use an electric fan drive in a utility vehicle, it is necessary to place the electric machine or motor in as favorable a position as possible. The volume of an electric motor is governed by the mechanical torque to be generated. Based on the power density, an electric motor offering the highest possible rotation speed is preferable. Engine compartments which are conventionally designed to drive the fan mechanically by the crankshaft via a belt drive do not permit the positioning of a direct-driving electric motor. A design alteration to the engine solely for this reason alone is out of the question.